1. Field of the Invention
The present invention relates to a method and to a system for visualizing the position and orientation of an object that is penetrating or has penetrated a subject.
2. Description of the Prior Art
In many technical applications, the problem occurs of making an object visible that has penetrated into a subject and is thus no longer visible, or is only partly visible, with respect to its position and orientation in the subject, e.g., for a person handling the object. In medical technology there is, for example, a problem of this sort in the removal of tissue from inside the body of a living being, using a biopsy needle that is to be guided by a physician to the point of the tissue to be examined in a manner that is as precise and closely monitored as possible. As a rule, guidance of the biopsy needle is accomplished using an imaging system, for example an x-ray computed tomography apparatus, a C-arm x-ray apparatus, or an ultrasound apparatus, with which images can be obtained from inside the body of the living subject, these images indicating the position and orientation of the biopsy needle relative to the tissue to be examined.
Advantages of the use of an x-ray computed tomography apparatus as an imaging system in the biopsy procedure are that in the visualization of the biopsy needle ensues in real time, and that good presentation of soft tissue parts occurs in images obtained using an x-ray computed tomography apparatus. In this way, the current position of the biopsy needle relative to the tissue to be examined can be visualized and measured. In addition, in the obtained images not only deformations of the biopsy needle during penetration into the body of the living being, but also pathological and anatomical characteristics of the imaged tissue, can for the most part be recognized clearly. A disadvantage in the use of an x-ray computed tomography apparatus is the relatively small diameter of the gantry opening, which does not present an optimal operating field for the execution of a biopsy procedure. Since in addition the hands of the physician carrying out the biopsy procedure are located within the x-ray projection fan of the x-ray computed tomography apparatus during the biopsy procedure, the physician is exposed to a significant radiation load.
The use of an x-ray apparatus, in particular a C-arm x-ray apparatus, as an imaging system for a biopsy procedure has the advantage that the radiation load for the physician guiding the biopsy needle is significantly less than in a biopsy procedure employing an x-ray computed tomography apparatus. In addition, more space is available for the biopsy procedure. Moreover, obtaining x-ray images using a C-arm x-ray apparatus is generally more economical than is the case with an x-ray computed tomography apparatus. A disadvantage of the x-ray images obtained using a C-arm x-ray apparatus is the two-dimensional representationxe2x80x94which is often insufficientxe2x80x94of the tissue to be examined, and the fact that tumors in x-ray images of this sort are often insufficiently recognizable or not recognizable at all.
Advantages of the use of ultrasound for imaging in the biopsy procedure are that the exposure method free of radiation load, and that the images are obtained in real time. However, a disadvantage is that the tissue to be examined cannot always be represented in ultrasound images. Problems in such imaging always result when media that cannot be penetrated by ultrasound, or can be penetrated by ultrasound only with difficulty, for example air or bone, are located between the ultrasound sending and receiving surfaces of the ultrasound apparatus and the tissue to be examined.
In order to compensate for the disadvantages of the individual imaging systems, it is known to obtain x-ray images in multiple exposures during the execution of a biopsy procedure, using a C-arm x-ray system and an x-ray computed tomography apparatus. However, the patient must be moved from one bed to another numerous times for the exposures using the C-arm x-ray apparatus and for the exposures using the x-ray computed tomography apparatus, which makes the execution of the biopsy procedure expensive and complicated. A further technological development involves the use of what are known as xe2x80x9csliding gantries,xe2x80x9d which refers to a coupling of an x-ray computed tomography apparatus with a C-arm x-ray apparatus. A patient bed supporting a patient can thereby be moved back and forth between the x-ray computed tomography apparatus and the C-arm x-ray apparatus for different diagnostic exposures without repositioning the patient.
In spite of this improvement, the execution of a biopsy procedure proves to be laborious due to the required movement back and forth of the patient between two imaging systems during a biopsy procedure.
German OS 198 07 884 discloses a method and an apparatus for obtaining intraoperative exposures of a subject under examination which are compared with exposures that are produced pre-operatively and/or intraoperatively.
In German OS 196 20 371, a method and an arrangement are disclosed in which, for example before a biopsy, a series of two-dimensional x-ray exposures are produced of a subject under examination, in particular to produce contrast-rich x-ray exposures of vascular structures using an imaging apparatus. Using a second imaging apparatus, a volume data set of the subject under examination is produced, from which a series of two-dimensional projections are generated, which visualize, in particular, contrast-rich structures of the subject under examination. Subsequently, the projections and the two-dimensional x-ray images are superposed to form a series of superposition images.
An object of the present invention is to provide a method and a system of the type described above wherein the visualization of an object that has penetrated into a subject is simplified.
According to the invention, this object is achieved in a method for visualizing the position and orientation of an object that is penetrating or has penetrated into a subject, wherein a first set of image data is produced from the interior of the subject, using a first apparatus for recording image data, before the object has penetrated into the subject, a second set of image data is produced from the interior of the subject, using a second apparatus, realized differently from the first apparatus, for recording image data while the object penetrates into the subject, or after the object has penetrated into the subject, a connection (linking relationship) between the image data of the first set and the image data of the second set is produced, image data of the first set are superimposed with image data of the second set in order to form a fused set of image data, and an image obtained from the fused set of image data is displayed.
The first apparatus for recording image data is preferably an apparatus with which image data for the production of high-quality images, correct in detail, from the interior of the subject can be obtained in a non-invasive manner. The second apparatus for recording image data is preferably fashioned such that images of the object that is penetrating or that has penetrated into the interior of the subject can be obtained non-invasively in an economical, simple and rapid manner. Using the first apparatus, image data are thereby obtained before the introduction of the object into the subject, and are stored. Using the second apparatus, image data are recorded, preferably in real time, during the introduction of the object into the subject, or after the object has been introduced into the subject. Finally, by producing a connection between the image data obtained using the first apparatus and the image data obtained using the second apparatus, in a registration method, and by superimposing the image data with one another, fused sets of image data are obtained from which images can be produced in real time, in which details from the interior of the subject are visible, and the object that has been introduced into the subject is visible as well. An application of the inventive method is the above-specified visualization of a biopsy needle that is penetrating or that has penetrated into the body of a living subject in a medical context. With the use of the inventive method, a movement back and forth of the living subject between two devices for recording image data during the biopsy procedure is not necessary, since image data for the visualization of the biopsy needle during the biopsy procedure are recorded using only one imaging system, and these data are fused with previously obtained image data in order to produce images that are effective in diagnosis.
The above object is also achieved in accordance with the invention in a system for visualizing the position and orientation of an object that is penetrating into a subject or that has penetrated into a subject, having a first apparatus for recording image data with which a first set of image data from the interior of the subject can be produced, a second apparatus, realized differently from the first apparatus, for recording image data with which a second set of image data from the interior of the subject can be produced, an arrangement for producing a connection between the image data of the first set and the image data of the second set, an arrangement for superposing image data of the first set with image data of the second set in order to produce a fused set of image data, and a display for graphically displaying an image obtained from the fused set of image data.
By providing an arrangement for producing a connection between image data of the first set and image data of the second set, and an arrangement for the superposition of image data, the inventive system enables the production of diagnostically effective images. During the introduction of the object into the subject it is necessary to obtain image data from the interior of the body of the subject using only one imaging system, in order to enable visualization of the position and orientation of the object in the subject. In this way, movement of the subject back and forth between first and second means for recording image data for the visualization of the object, as described above for the case of a biopsy procedure in a medical context, is avoided.
In an embodiment of the inventive system, the first apparatus is an x-ray computed tomography apparatus. The second apparatus is an x-ray apparatus having an x-ray source that emits a cone-shaped x-ray beam bundle, and a planar x-ray beam detector, in particular a C-arm x-ray apparatus, and/or an ultrasound apparatus provided with an ultrasound head, with which sets of two-dimensional and/or three-dimensional image data can be obtained. Using the x-ray computed tomography apparatus, high-resolution images, true to detail, from the interior of a subject can thereby be obtained. The C-arm x-ray apparatus and the ultrasound apparatus are distinguished in that images from the interior of a subject can be produced in real time in a simple, rapid, and economical manner.
Suitable registration methods, that can be executed by a computer for connecting the image data recorded using the first and second apparatuses are of the types known as landmark-based registration methods (cf. R. Boesecke, Th. Bruckner, G. Ende: xe2x80x9cLandmark based correlation of medical images,xe2x80x9d Phys. Med. Biol., 1990, vol. 35, no. 1, pp. 121-126), fully automated voxel-based registration methods (cf. C. Studholme, D. L. G. Hill, D. J. Hawkes: xe2x80x9cAutomated three-dimensional registration of magnetic resonance and positron emission tomography brain images by multiresolution optimization of voxel similarity measures,xe2x80x9d United Medical and Dental Schools of Guy""s and St. Thomas""s Hospitals, 1996, or Colin Studholme: xe2x80x9cMeasures of 3D Medical Image Alignment, Ph.D. thesis,xe2x80x9d United Medical and Dental Schools of Guy""s and St. Thomas""s Hospitals, 1997), elastic registration methods (cf. Lee, Seungyong, G. Wolberg, S. Y. Shin: xe2x80x9cScattered Data Interpolation with Multilevel B-Splines,xe2x80x9d IEEE Transactions on Visualization and Computer Graphics, 3(3), pp.337-354,1997), or 2D, 3D registration methods (cf. G. P. Penney, J. Weese, J. A. Little, P. Desmedt, et al.: xe2x80x9cA Comparison of Similarity Measures for Use in 2-D-3-D Medical Image Registrationxe2x80x9d: IEEE Transactions on Medical Imaging, 1998, vol. 17, no. 4, pp. 586-595). In registration method of this sort, a transformation rule is determined in order to enable the image data obtained using the first apparatus and the image data obtained using the second apparatus to be superimposed with each other. In addition, the execution of a registration method is required whenever the orientation of the apparatus provided for recording image data in real time changes relative to the subject. Thus, if the projection geometry of the C-arm x-ray apparatus relative to the subject changes, or the position and/or orientation of the ultrasound head relative to the subject changes, then as a rule a new connection of the image data newly recorded using the C-arm x-ray apparatus, or the image data newly recorded using the ultrasound head, with the image data previously recorded using the x-ray computed tomography apparatus must take place in the form of a registration procedure.
In a preferred specific embodiment of the invention the second apparatus is an ultrasound apparatus, and a position acquisition system is used with which the position of the ultrasound head of the ultrasound apparatus can be continuously acquired. In this way, a registration method for connecting image data obtained using the x-ray computed tomography apparatus and the ultrasound image data need to be carried out only once, at the beginning of a visualization procedure, because with the aid of the position acquisition system, position changes of the set of ultrasound image data, recorded using the ultrasound apparatus, relative to the subject are continuously determined, and the connection with the image data recorded using the x-ray computed tomography apparatus can be adapted corresponding to the current position of the ultrasound head.